Different types of audio signals are received at and sent from a vehicle. For instance, downlink signals are received from some other location. Uplink signals are sent from the vehicle to some other destination. Speakers broadcast the downlink speech signals that are received, and microphones receive the speech of occupants in the vehicle for transmission. As different speech signals are transmitted and received, these signals may be reflected in the vehicle or at other places, and echoes can occur. The presence of echoes degrades the quality of speech for listeners and echo cancellers have been developed to attenuate echoes.
Acoustic echo cancellers are typically used in vehicles as part of hands-free equipment due to the close proximity of loud speakers with open microphones. However, echo cancellers can typically provide only a portion of the cancellation required in vehicular environments because of the high coupling between the loud speakers and the microphones. As a result, echo suppression approaches are used in addition to echo cancellers to increase the attenuation of echoes to an acceptable level.
As mentioned, acoustic echo cancellers are often a part of the hands free automotive environment. The amount of time required to locate and cancel an echo is typically referred to as the convergence time. Accurate convergence control is necessary to effectively remove the resulting echo. However, previous attempts at reliable convergence control in the often harsh automotive environment faced many difficulties. For instance, the control mechanism had to be able to adapt quickly to a rapidly changing acoustic environment and also had to be able to cope with high noise energy. Previous methods for controlling the convergence in vehicular environments generally failed to achieve these goals. As a result, echo continued to degrade speech signals and user satisfaction with these systems was adversely affected.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.